Such construction machines are known from practice. They normally have a primary drive which emits exhaust gases. Due to anti-pollution guidelines and laws becoming stricter, subsequent treatment measures which reduce harmful or undesired ingredients of the exhaust gases are increasingly required. One possible measure is to inject additives into the exhaust stream. By various chemical reactions, the undesired ingredients of the exhaust gases are converted into less harmful substances. One example of this is the injection of urea solutions into the exhaust gases of diesel engines to reduce the emission of various nitrogen oxides.